DE2056011C3 - Write control device in a magnetic tape unit - Google Patents

Description

There are control devices in a magnetic tape unit known with a write head and a read head, in which by the write head on one Data recorded on magnetic tape can be read by the read head to check whether the data is on recorded accurately or not on the magnetic tape. Check these known control devices however only the recorded data and do not control the write head or the write circuit.

The known control devices can be classified into the following three systems: One Control device for controlling whether data is recorded on the magnetic tape or not, so that binary signals "1" and "0", which show the recorded data, can be precisely distinguished from one another can; a parity check means for checking whether each column of the recorded data has the Data bits along the parity check bit, which is determined by whether the number of Data bits of "I" or "0" of each of the columns making up the data block are odd or even; and a Echo control device which takes advantage of the fact that the bit formation is determined so that more than one "1" bit can always be present in the data of a column, and which checks whether there is more than one "!" Bit always is present or not in each of the columns of the data written on a magnetic tape. at These control devices are, however, if the write head and the write circuit are faulty, even if a write command is given, the old data recorded on the magnetic tape will not be erased and no new data can be recorded on the tape, so the read head retains the old Reads data on the tape and checks the old data from these points of view. But if a If there is an error in the old data, the error may be in the write head and the write circuit cannot be found.

The invention is based on the task of checking for errors that occur before and after the start or. End signal of a data block are to be executed. The task is solved by the features of the Claim 1.

According to the invention, after a set time has elapsed after the start signal, the The presence of the block signals is checked until the end signal occurs. The invention thus enables also a detection of errors in the write head and in the write circuit.

Preferred refinements of the invention are given in the subclaims.

An exemplary embodiment of the invention is described with reference to the drawing, are in

Fig. I is a Zeildiagramtn to explain the Device of the invention,

F i g. 2 shows an embodiment of the device according to the invention and

FIG. 3 is a timing diagram of the embodiment of FIG. 2.

In Fig. 1 are 11 to 16 time courses which the Alternation between the beginning of writing and the end of reading on the magnetic tape show recorded data. The time courses 11 to 16 explains the communication between the reading head and the recorded data when the data is on the magnetic tape can be written by the write head and the magnetic tape in the by the arrow

' ¹ ^ indicated direction is advanced. Writing begins at 11 and then state 12 is reached when line Ti has been passed. »Ei ti and 12 data are not read because the data is being read by the read head

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have not achieved. In other words, no data has to be read from the read head in states 11 and 12. If data in the states II and 12 are read, it means that the old data has not been erased but has remained on the magnetic tape and that the write operation has not been carried out normally. State 13 is reached when time T _{2 has passed} from state 12, and in this state 13 the data must be read by the read head, since the data has arrived at the read head. If data in the state 13 cannot be read, it means that there is an error in the writing system and that writing is not carried out smoothly. If the data is written smoothly, the data in state 13 can be read. As far as data is written continuously, the data is read by the reading head at 14 with a difference in time delay. When the data to be read reach an end, no data is written by the write head, but the data is read by the read head until the time Γι has passed, that is, until state 15 is reached and then state 16 is reached after the Time T _{2 has} passed and no data is read after that. The time period between the time Γι and the time Γι + Ti is used to eliminate the skew of the data on the magnetic tape and a misreading due to the expansion and contraction of the tape. This method makes it possible to use the delay times T 1 and Γ 2 to check whether the written data has been read accurately by the read head or not, and also to judge whether or not the write operation has been carried out normally.

In the embodiment of the invention, FIG. 2, 17 is an inter-block gap finding circuit. 18 is a delay counter, 19 is a flip-flop and 21 to 29 are read detection circuits, each of the read detection circuits 21 to 29 sending out an output "1" when a read signal is present in the corresponding track and sending out an output "0", if there is no read signal in the corresponding track. 38, 39, 41 and 42 are nionosmbilc multivibrators. 38 and 41 are the first and third delay circuits for generating the delay time T 1, and 39 and 42 are the second and fourth delay circuits for generating the delay time T ₂ . 30, 34, 35 and 36 are “OR” circuits, 31 and 33 are first and / or “AND” circuits, 32 is an inverter, and 37 and 40 are the first and second flip-flops.

3 is a timing diagram for explaining the circuit of FIG. 2, FIG. 2 showing an embodiment of the invention which is provided in a system comprising a central processing unit CPU, a channel arrangement "channel", a magnetic tape controller MTC and a magnetic tape unit A-TTL / contains.

Assuming first that a write command from the central processing unit CPU will be given to the channel arrangement "channel", the channel arrangement "channel" resets the flip-flop 19 in accordance with the write command to send a tape drive signal from the flip-flop 19 to the magnetic tape unit MTU to start the drive of the magnetic tape ^fi 5. At the same time, the tape drive signal is sent to the delay counter 18 to operate this delay counter 18, and then the start signal is sent with the first delay time and the start signal is sent out with a second delay time from the first delay time. The read start signal is sent via the "OR" circuit 35 and sets the flip-flop 37 "on". With the second delay time, writing is then started by the write start signal and the write signal then switches the flip-flop 37 "off" via the:> OR "circuit

36 with a delay time of 7i generated by the monostable multivibrator 38. An error signal is sent to the channel arrangement "channel" if the read signals 1 to 9 of one of the tracks during the time period between the time at which the flip-flop 37 is switched "on" and the time at which the flip-flop 37 is switched "on". Flop 37 is switched "off", that is, between the time the data begins to be recorded on the magnetic tape by the write head and the time the data arrives at the read head. If the time T has passed ₂ after the flip-flop

37 is switched “off”, the flip-flop 40 is switched off by the output signal from the monostable multivibrator 39 "switched on. Even if read signals 1 to 9 are supplied from the plurality of channels, one or all outputs of read discovery circuits 21 through 29 are "1" and the output appears on the "OR" circuit 30 under the condition that flip-flop 40 is "on" with the output signal through the inverter 32 is reversed so that coincidences through the "AND" circuit 33 are not obtained can and no error signal is sent.

Next, when a write stop command is given from the central processing unit CPU to the channel arrangement "channel", an end-of-write signal is sent from the channel arrangement "channel" to the magnetic tape control device MTC. This signal is delayed by the mono-stable multivibrator 41 by the time Γι and sets the flip-flop 40 "on".

Therefore, reading of the recorded data is continued for the time T \ after the end of writing and no error signal is sent out if any of the read signals 1 to 9 is supplied during the time T ₂ after the time T \. After the time T _{2 has} elapsed, the flip-flop 37 is "on" via the "OR" circuit 35 by the output signal from the monostable multivibrator 42. Therefore, if the read signal is applied to the "AND" circuit 31 via the "OR" circuit 30, no error signal is sent out. If the read signal is asserted when flip-flop 37 is "on", the error signal is sent out to indicate that the write operation has not been performed normally. The error signal is sent out because no data is allowed to be recorded where writing has not been carried out.

When the reading of the recorded data by the reading head is next finished, the Interblock gap detection circuit issues a final reset signal to stop the eland drive signals the flip-flop 19 and resets the flip-flop 37 via the "OR" circuit 36. Through the foregoing Operation completes the operation of the circuit according to the invention. About the channel arrangement The error signal sent through the "OR" circuit 34 is sent to the memory and operates to the Write data again by executing the program.

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According to the invention, it can always be surely found out whether the write operation is carried out normally has been or not, and by using the write control device of the invention in a Magnetbandeir.iieit in a data processing system can improve the reliability of the entire data processing system including the magnetic tape unit noticeably improved.

For this purpose 3 sheets of drawings

Claims (5)

20 56 Oil claims: 1. Write control device in a magnetic tape unit to detect errors before and according to the start or end signal of a data block, characterized in that the start signal a device starts that for a preset time (Ti) on freedom of signals and after checks for the presence of the dlock signals during this time and generates error signals if during the signals occur at the read head at a preset time and no signals occur after this time, and that the end signal starts another device that is present for the preset time (Ti) of the block signals and after this time checks for freedom from signals and generates error signals, if no signals appear on the read head during the preset time and signals after this time appear. 2. Write control device according to claim 1, characterized by a first delay circuit (38) with a delay time equal to first time period (Ti), which is started by the write start signal, by a first flip-flop (37), which is reset by the output of the first delay circuit (38) and by the Reading start signal is set, and by a first »ANDw circle (31) to the» AND «output the setting side of the first flip-flop and the "OR" output of the read signals from a plurality to get from traces. 3. Write control device according to claim 2, characterized by a second delay circuit (39) with a time delay equal to a second time period (T2), which is started by the output of the first delay circuit (38), by a second flip-flop (40), the is set by the output of the second delay circuit (39), by a second "vJND" circuit (33) to get the "AND" output of the setting side of the second flip-flop (40), and by an inverter (32 ) to reverse the "OR" output of the read signals from a plurality of tracks. 4. write control device according to claim 3, characterized by a third delay circuit (41) with a delay time equal to first time period (Ti) started by the write stop command, the second flip-flop (40) is reset by the output of the third delay circuit (41). 5. write control device according to claim 4, characterized by a fourth delay circuit (42) with a delay time equal to the second time period (Tj) determined by the output of the third delay circuit (41) is started, the first flip-flop (37) through the output of the fourth delay circuit (42) is set.